08 java chapter7

8/12/2019 08 Java Chapter7

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207

CHAPTER

7CHARACTERS, STRINGS, AND THE

STRINGBUFFERIn this section, you will:

Manipulate characters

Declare a String object

Compare String values

Use other String methods

Convert Strings to numbers

Learn about the StringBuffer class

Ican write an interactive program that accepts a character, but I really wantto be able to manipulate characters and let users enter words or numbersinto programs, you announce to Lynn Greenbrier, your Java mentor.

You need to learn about the String, Lynn says.The wide variety of String

methods provided with the Java programming language will help you use words

and phrases efficiently.Youll even be able to let your users input numbers.


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PREVIEWING A GUESSING GAME PROGRAMTo demonstrate the use of the String methods, you will test a simple guessing game, sim-ilar to Hangman. The user first will guess letters, and then guess the motto of EventHandlers Incorporated.

To preview the guessing game:

1. Open theChap7SecretPhrase.java file in the Chapter.07 folder on yourStudent disk.

2. At the command prompt, compile the class with the command javacChap7SecretPhrase.java.

3. Run the program with the command java Chap7SecretPhrase. Enterkeyboard characters one at a time and guess Event Handlers motto.

MANIPULATING CHARACTERSYou learned in Chapter 2 that the char data type is used to hold any single character. Inaddition to the primitive data type char, Java offers a Character class.The Character classcontains standard methods for testing the values of characters, such as letters or digits.

Method Description

isUpperCase() Tests if character is uppercase

toUpperCase() Changes a lowercase character to uppercase

isLowerCase() Tests if character is lowercase

toLowerCase() Changes an uppercase character to lowercase

isDigit() Returns true if the argument is a digit (0-9) and false otherwise

isLetter() Returns true if the argument is a letter and false otherwise

isLetterOrDigit() Returns true if the argument is a letter or digit and false otherwise

isWhitespace() Returns true if the argument is whitespace and false otherwise. (Thisincludes the space, tab, newline, carriage return, and form feed.)

Ta e 7-1 Common met o s o t e C aracter c ass

Figure 7-1 Structure of the Character class

Java.lang.Object

+--java.lang.Character

208 Chapter 7 Characters, Strings, and the StringBuffer


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Manipulating Characters 209

Figure 7-1 shows the Character class is defined in java.lang.Object and is automaticallyimported into every program you write. Commonly used methods available in theCharacter class are shown in Table 7-1.

Figure 7-2 contains a program that uses many of the methods shown in Table 7-1.Theprogram declares a character variable named aChar and allows the user to supply a value

for aChar by entering a single character from the keyboard.The program tests aChar usinga series of if and ifelse statements to determine whether the entered character is adigit, letter, or whitespace, and if it is a letter, whether it is lowercase or not.

Figure 7-2 The TestCharacter program

public class TestCharacter

{

public static void main(String[] args)throws Exception

{

char aChar;

System.out.println("Please enter a character");

aChar = (char)System.in.read();

System.in.read();System.in.read();if(Character.isDigit(aChar))

System.out.println(aChar+"is a number");

else System.out.println(aChar+"is not a number");

if(Character.isWhitespace(aChar))

System.out.println(aChar+ "is a letter");

else System.out.println(aChar+ "is not a letter");

if(Character.isWhitespace(aChar))

System.out.println

("Character is a whitespace character");

else System.out.println

("Character is not a whitespace character");

if(Character.isLetter(aChar))

if(Character.isLowerCase(aChar))

System.out.println(aChar+

" is lowercase character");

else

System.out.println(aChar+

" is not a lowercase character");

}

}


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The output of the TestCharacter program for sample keyboard input of an uppercasecharacter C is shown in Figure 7-3.

DECLARING A STRING OBJECTYou learned in Chapter 1 that a sequence of characters enclosed within double quota-tion marks is a literal string.You have used many literal str ings, such as First Java pro-gram, within println() statements.

You also use String in main() method headers.

A String variable is simply an object of the class String. The class String is defined injava.lang.String, which is automatically imported into every program you write. Figure 7-4shows that the String class descends directly from the Object class.The Str ing itself is dis-

tinct from the variable you use to refer to it.You create a String object by using the key-word newand the String constructor method, just as you would create an object of anyother type. For example, String aGreeting = new String("Hello"); is a state-ment that defines an object named aGreeting, declares it to be of type String, and assignsan initial value of Hello to the String. The variable aGreeting stores a reference to a

String objectit keeps track of where the String object is stored in memory.When you

declare and initialize aGreeting, it links to the initializing String value. Alternately, youcan declare a String containing Hello with String aGreeting = "Hello";.Unlike other classes, the String class is special because you can create a String object with-out using the keyword newor calling the class constructor.

Tip

Figure 7-3 Sample output of the TestCharacter program



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Comparing String Values 211

After declaring a String, you can display it in a print() or println() statement, just as youwould for any other variablefor example,System.out.println("The greetingis " + aGreeting);.

COMPARING STRING VALUESIn the Java programming language, String is a class, and each created String is a classobject. A String variable name is a reference; that is, a String variable name refers to alocation in memory, rather than to a particular value.

The distinction is subtle, but when you declare a variable of a basic, primitive type, suchas int x = 10;, the memory address where x is located holds the value 10. If you laterassign a new value to x, for example,x = 45;, then 45 replaces 10 at the assigned mem-

ory address.When you declare a String, such as String aGreeting = "Hello";,aGreeting holds a memory address where the characters Hello are stored. If you subse-quently assign a new value to aGreeting, such as aGreeting = "Bonjour";, then theaddress held by aGreeting is altered; now aGreeting holds a new address where the char-acters Bonjour are stored.Bonjour is an entirely new object created with its own loca-

tion. The Hello String is still in memory; its just that aGreeting no longer holds itsaddress. Eventually, a part of the Java system called the garbage collector will discard the

Hello characters. Strings, therefore, are never actually changed; instead, new Strings arecreated and String variables hold the new addresses. Strings and other objects that cantbe changed are known as immutable.

Because String variables hold memory addresses, you cannot make a simple comparisonto determine whether two String objects are equivalent. For example, if you declare twoStrings as String aGreeting = "Hello"; and String anotherGreeting ="Hello";, Java will evaluate a comparison, such as if(aGreeting ==

anotherGreeting) as false. This is because when you compare aGreeting toanotherGreeting with the == operator, you are comparing their memory addresses, nottheir values.

Fortunately, the String class provides you with a number of useful methods.The equals()method evaluates the contents of two String objects to determine if they are equivalent.The method returns true if the objects have identical contents. For example, Figure 7-5

shows two String objects and several comparisons. Each comparison in Figure 7-5 is true;each results in printing the line Names the same.

Figure 7-4 Structure of the String class

Java.lang.Object

+--java.lang.String


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The String class equals() method returns true only if two Strings are identi-

cal in content. Thus, a String holding Roger (with a space after the r) is not

equivalent to a String holding Roger (with no space after the r).

Each String shown in Figure 7-5 (aName and anotherName) is an object of type String,so each String has access to the String class equals() method.The aName object can callequals() with aName.equals(), or the anotherName object can call equals() withanotherName.equals().The equals() method can take either a variable String object

or a literal string as its argument.

The equalsIgnoreCase() method is similar to the equals() method.As its name implies,it ignores case when determining if two Strings are equivalent. Thus,aName.equals("roGER") is false, but aName.equalsIgnoreCase("roGER")is true.This method is useful when users type responses to prompts in your programs.You cannot predict when a user might use the Shift key or the Caps Lock key dur ingdata entry.The equalsIgnoreCase() method allows you to test entered data without regard

to capitalization.

When the compareTo() method is used to compare two Strings, it provides additional

information to the user in the form of an integer value.When you use compareTo() tocompare two String objects, the method returns zero only if the two Strings hold thesame value. If there is any difference between the Strings, a negative number is returnedif the calling object is less than the argument, and a positive number is returned if thecalling object is more than the argument. Strings are considered less than or more

than each other based on their Unicode values; thus,a is less than b, and b is lessthan c.

For example, if aName holds Roger, then aName.compareTo("Robert"); returnsa 5. The number is positive, indicating that Roger is more than Robert. This doesnot mean that Roger has more characters than Robert; it means that Roger isalphabetically more than Robert.The comparison proceeds as follows:

The R in Roger and the R in Robert are compared, and found to be equal.

The o in Roger and the o in Robert are compared, and found to be equal.

Tip

Figure 7-5 String comparisons using the equals() method

String aName = "Roger";

String anotherName = "Roger";

if(aName.equals(anotherName))

System.out.println("Name's the same");

if(anotherName.equals(aName))

System.out.println("Name's the same");

if(aName.equals("Roger");System.out.println("Name's the same");



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Using Other String Methods 213

The g in Roger and the b in Robert are compared; they are different.Thenumeric value of g minus the numeric value of b is 5 (because g is five lettersafter b in the alphabet), so the compareTo() method returns the value 5.

Often you wont care what the specific return value of compareTo() is; you simply willwant to determine if it is positive or negative. For example, you can use a test, such as

if(aWord.compareTo(anotherWord)


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Another method is available to convert any primitive type to a String. If you declare aString as anotherString and a float as float someFloat = 12.34f, thenanotherString = "" + someFloat, assigns the String 12.34 to anotherString.

The Java interpreter first converts the float 12.34f to a String 12.34, and adds it to thenull String . Joining Strings is called concatenation. The resulting string 12.34 is

then assigned to anotherString.

The toString() method is not part of the String class; it is a method included

in Java that you can use with any type of object. You have been using

toString() throughout this book without knowing it. When you use print() and

println(), their arguments are automatically converted to Strings if necessary.

You dont need import statements to use toString() because it is part of

java.lang, which is imported automatically.

Because the toString() method takes arguments of any primitive type, includ-

ing int, char, double, and so on, it is an overloaded method.

You already know that you can join Strings with other Strings or values by using aplus sign (+); you have used this approach in println() statements since Chapter 1.For example, you can print a firstName, a space, and a lastName withSystem.out.println(firstName + " " + lastName);. Additionally, you can

extract part of a String with the substring() method, and use it alone or concatenate itwith another String.The substring() method takes two argumentsa start position andan end positionthat are both based on the fact that a Strings first position is positionzero. For example, the program segment in Figure 7-6 shows the names Mondaythrough Friday as Strings representing the days of the week. An abbreviation of aweekday, Monday for example, can be printed after using the substring

method System.out.println("The abbreviation for Monday is " +

monday.substring(0,3));. Here monday.substring(0,3) starts at the firstcharacter (index of 0), and extracts the first three letters from the string stored asMonday. The output of the weekday abbreviations program is shown in Figure 7-7.

Tip

Tip



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To demonstrate the use of the String methods, you will create a simple guessing game,similar to Hangman.The user first will guess letters, and then attempt to guess the mottoof Event Handlers Incorporated.

To create the guessing game:

1. Open a new text file in your text editor. Enter the following first few lines ofa SecretPhrase program.The program will contain the target phrase that theuser will try to guess (Plan With Us), as well as a display phrase that ismostly asterisks (with a few hints).

public class SecretPhrase{ public static void main(String[] args) throws Exception { String targetPhrase = "Plan With Us"; String displayPhrase = "P*** W*** U*";

2. Add the following variables that will hold the users guess and the position of

a guess that is found within the phrase:

char guess;int position;

3. Next, add the following brief instruction:

System.out.println("Play our game - guess our motto");

4. Enter the statement to display the hint phrase:

System.out.println(displayPhrase);

5. Add the following loop that continues while asterisks remain in thedisplayPhrase.The user will enter a letter.You will use the indexOf() methodto determine whether the guessed letter appears in the targetPhrase. If it doesnot, then ask the user to guess again. If the guessed letter appears in thephrase, you reconstruct the display phrase with the following:

The substring of characters in the display phrase that comes before thecorrect guess

The correct guess

The substring of characters in the display phrase that appears after the correctguess; in other words, the correct letter replaces the appropriate asterisk

Add the following code:

while(displayPhrase.indexOf('*') != -1){ System.out.println("Enter a letter"); guess = (char)System.in.read();



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Converting Strings to Numbers 217

System.in.read(); System.in.read(); // Absorbs Enter key position = targetPhrase.indexOf(guess); // Determines position of guess if(position == -1) // If guess is not in target phrase System.out.println("Sorry, guess again");

else // If guess is in target phrase { displayPhrase = displayPhrase.substring(0,position) + guess + displayPhrase.substring (position+1,displayPhrase.length()); System.out.println(displayPhrase); }}

6. Thewhile loop will continue until all the asterisks in the targetPhrase arereplaced by correct letters.Therefore, after the closing curly brace for thewhile loop, enter:

System.out.println("Congratulations!");.

7. Type the closing curly braces for the main() method and for theSecretPhrase class.

8. Save the program as SecretPhrase.java in the Chapter.07 folder on yourStudent Disk, then compile and run the program. Make sure you understandhow all the String methods contribute to the success of this program.

CONVERTING STRINGS TO NUMBERSIf a String contains all numbers, as in 649, you can convert it from a String to a num-ber so you can use it for arithmetic, or use it like any other number.To convert a Str ing

to an integer, you use the Integer class, which is part of java.lang and automaticallyimported into programs you write.The parseInt() method is part of the Integer class,and takes a String argument and returns its integer value. For example, int anInt =Integer.parseInt("649"); stores the numeric value 649 in the variable anInt.Youcan then use the integer value just as you would any other integer.

The word parse in English means to resolve into component parts, as when

you parse a sentence. In Java, to parse a String means to break down its

separate characters into a numeric format.

It is also easy to convert a String object to a double value.You must use the Double class,

which, like the Integer class, is also imported into your programs automatically.A methodof the Double class is parseDouble(), which takes a String argument and returns its doublevalue. For example, double doubleValue = Double.parseDouble("147.82");stores the numeric value 147.82 in the variable doubleValue.

Tip


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To convert a Str ing containing 147.82 to a double, you can use the following code:

String stringValue = new String("147.82");Double tempValue = Double.valueOf(stringValue);double value = tempValue.doubleValue();

The stringValue is passed to the Double.valueOf() method, which returns a Doubleobject. The doubleValue() method, is used with the tempValue object. This methodreturns a double that is stored in value.

The Double and Integer classes are examples of wrappers. A wrapper is a

class or object that is wrapped around a simpler thing. You use the Double

(uppercase D) class to make it convenient to work with primitive double

(lowercase d) variables.

When planning an event, Event Handlers Incorporated must know how many guests to

expect.Next you will prompt the user for the number of guests, read characters from the

keyboard, store the characters in a String, and then convert the String to an integer.To create a program that accepts integer input:

1. Open a new text file in your text editor. Type the statement importjavax.swing.*;, press [Enter], and then enter the following first fewlines of a DialogInput class that will accept string input:

public class NumInput{ public static void main(String[] args) throws Exception {

2. Declare the following variables to hold the input String and the resultinginteger:

String inputString;int inputNumber;

3. Enter the following input dialog box statement that stores the user keyboardinput in the String variable inputString:

inputString = JOptionPane.showInputDialog(null, "Enter the number of guests at your event");

4. Use the following Integer.parseInt() method to convert the input String to aninteger.Then use the integer in a numeric decision that displays a message

dialog box when the number of guests entered is greater than 100:inputNumber = Integer.parseInt(inputString);if(inputNumber > 100) JOptionPane.showMessageDialog(null,

"A surcharge will apply!);

Tip



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Learning About the StringBuffer Class 219

5. Enter the closing statement System.exit(0); press [Enter], and thenenter the final two closing curly braces for the program.

6. Save the program as NumInput.java in the Chapter.07 folder on yourStudent Disk, then compile and test the program.

LEARNING ABOUT THE STRINGBUFFER CLASSA String class limitation is that the value of a String is fixed after the String is created;

Strings are immutable.When you write someString = "Hello"; and follow it withsomeString = "Goodbye";, you have neither changed the contents of computermemory at someString, nor have you eliminated the characters Hello. Instead, youhave stored Goodbye at a new computer memory location and stored the new addressin the someString variable. If you want to modify someString from Goodbye toGoodbye Everybody, you cannot add a space and Everybody to the someString that

contains Goodbye. Instead, you must create an entirely new String, Goodbye

Everybody, and assign it to the someString address.

To circumvent these limitations, you can use the StringBuffer class.StringBuffer is analternative to the String class, and can usually be used anywhere you would use a String.The structure of the StringBuffer class is shown in Figure 7-8. Like the String class, theStringBuffer class is part of the java.lang package and is automatically imported intoevery program.

You can create a StringBuffer object that contains a given String with the statementStringBuffer eventString = new StringBuffer("Event Handlers

Incorporated");. When you initialize a StringBuffer object you must use thekeyword newand provide an initializing value between parentheses.You can create the

StringBuffer variable using syntax similar to the syntax for creating a String variable,such as StringBuffer philosophyString = null;.The variable does not referto anything until you initialize it with a defined StringBuffer object. For example,you could write philosophyString = new StringBuffer("Dedicated tomaking your event a most memorable one");.You can also initialize theStringBuffer variable philosophyString with an existing StringBuffer object usingphilosophyString = eventString;.

Generally when you create a String object, sufficient memory is allocated to accom-modate the number of Unicode characters in the string. A StringBuffer object, however,contains a memory block called a buffer which might not contain a string. Even if it

Figure 7-8 Structure of the StringBuffer class

Java.lang.Object

+--java.lang.StringBuffer


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does contain a String, the String might not occupy all of the buffer. In other words, thelength of a String can be different from the length of the buffer.The actual length ofthe buffer is referred to as the capacity of the StringBuffer object. It is generally more

efficient to make the StringBuffer capacity sufficient for the needs of your program,rather than modify a String that has been originally stored with a small capacity.

You can change the length of a String in a StringBuffer object with the setLength()method. The length is a property of the String held by the StringBuffer. When youincrease a StringBuffer objects length to be longer than the String it holds, the extracharacters contain \u0000. If you use the setLength() method to specify a lengthshorter than its String, the string is truncated.

To find the capacity of a StringBuffer object, you use the capacity() method. For exam-ple, the EventStringBuffer program in Figure 7-9 shows the creation of the eventString

object as StringBuffer eventString = new StringBuffer("Event

Handlers Incorporated");.The capacity of the StringBuffer object is obtained asint aCapacity = eventString.capacity(); and printed using

System.out.println("The capacity is " + aCapacity);. Figure 7-10shows the StringBuffer capacity is 43. Note that the capacity of 43 is 16 characters largerthan the length of the string Event Handlers Incorporated, which contains 27.

In general, when a StringBuffer object is created from a String, the capacity

will be the length of the string plus 16.

In Figure 7-9 the philosophyString variable is created as StringBufferphilosophyString = null;.The variable does not refer to anything until it is ini-

tialized with the defined StringBuffer object philosophyString = newStringBuffer("Dedicated to making your event a most memorableone");.The capacity of philosophyString is shown in Figure 7-10 as the length of thestring plus 16 or 67.

In the program shown in Figure 7-9, the length of the eventString is changed with thestatement eventString.setLength(40);. When the value of the length prints, asshown in Figure 7-10, the extra characters show as blanks before the String end isprinted. Also in Figure 7-10, the philosophyString length is shortened to a length of 30in the statement philosophyString.setLength(30);.The shortened 30-character

output string is shown as Dedicated to making your event in Figure 7-10.

Tip



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Using StringBuffer objects provides more flexibility than Str ing objects because you caninsert or append new contents into a StringBuffer.The StringBuffer class provides you

with three constructors:

public StringBuffer() constructs a StringBuffer with no charactersand a default size of 16 characters

public StringBuffer(int length) constructs a StringBuffer with nocharacters, and a capacity specified by length

Figure 7-10 Output of the EventStringBuffer program

Figure 7-9 EventStringBuffer program

public class EventStringBuffer

{

public static void main(String[] args)

{

StringBuffer eventString =

new StringBuffer("Event Handlers Incorporated");

int aCapacity = eventString.capacity();System.out.println("The capacity is " + aCapacity);

StringBuffer philosophyString = null;

philosophyString =

new StringBuffer("Dedicated to making your event a most memorable one");

int bCapacity = philosophyString.capacity();

System.out.println("The capacity is " + bCapacity);

eventString.setLength(50);

System.out.println("The eventString is " + eventString + "end");

philosophyString.setLength(30)

System.out.println("The philosophyString is " + philosophyString);}

}


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public StringBuffer(String s) contains the same characters as thosestored in the String object s (The capacity of the StringBuffer is the lengthof the String argument you provide, plus 16 additional characters.)

The append() method lets you add characters to the end of a StringBuffer object.For example, if a StringBuffer object is declared as StringBuffer someBuffer =

new StringBuffer("Happy");, then the statement someBuffer.append(" birthday") alters someBuffer to hold Happy birthday.

The insert() method lets you add characters at a specific location within a StringBufferobject. For example,if someBuffer holds Happy birthday, then someBuffer.insert(6,"30th "); alters the StringBuffer to contain Happy 30th birthday.The first character inthe StringBuffer object occupies position zero.To alter just one character in a StringBuffer,you can use the setCharAt() method. This method requires two arguments, an integerposition, and a character. If someBuffer holds Happy 30th birthday, thensomeBuffer.setCharAt(6,'4'); changes the someBuffer value into a 40th birthdaygreeting.

Next you will use StringBuffer methods.

To use StringBuffer methods:

1. Open a new text editor file, and type the following first lines of aDemoStringBuffer class:

public class DemoStringBuffer{ public static void main(String[] args) {

2. Use the following code to create a StringBuffer variable, and then call a

print() method (that you will create in Step 7) to print the StringBuffer:

StringBuffer str = new StringBuffer("singing");print(str);

3. Enter the following append() method to add characters to the existingStringBuffer and print it again:

str.append(" in the dead of ");print(str);

4. Enter the following insert() method to insert characters, print, insert addi-tional characters, and print the StringBuffer again:

str.insert(0, "Black");print(str);str.insert(5, "bird ");print(str);

5. Add one more append() and print() combination:

str.append("night");print(str);



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6. Add a closing curly brace for the main() method.

7. Enter the following print() method that prints StringBuffer objects:public static void print(StringBuffer s){ System.out.println(s);

}

8. Type the closing curly brace for the class, and then save the file asDemoStringBuffer.java in the Chapter.07 folder on your Student Disk.Compile and execute, and then compare your output to Figure 7-11.

You can extract characters from a StringBuffer object using the charAt()and getChars()methods.The charAt() method accepts an argument that is the offset of the characterposition from the beginning of a String. If you declare StringBuffer text = newStringBuffer("Java Programming");, then text.charAt(5) refers to thecharacter P.

If you try to use an index less than 0 or greater than the index of the last posi-

tion in the StringBuffer object, you will cause an exception to be thrown and

your program will terminate.

Finally, you can change a single character in a StringBuffer object using the setCharAt()method with two arguments.The first argument indicates the index position of the char-acter to be changed; the second argument specifies the replacement character. If you

declare StringBuffer text = "java";, the statement text.setCharAt(0,'J')sets the first character to J.

Tip

Figure 7-11 Output of the DemoStringBuffer program


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CHAPTER SUMMARY A sequence of characters enclosed within double quotation marks is a literal string.

You create a Str ing object by using the keyword newand the String construc-tor method.

Each String is a class object, and a String variable name is actually a reference.Strings, therefore, are never changed; they are immutable.

The equals() method evaluates the contents of two String objects to determinewhether they are equivalent, and then returns a Boolean value.

The equalsIgnoreCase() method determines if two Strings are equivalent withoutconsidering case.

The compareTo() method returns zero if two String objects hold the same value.Anegative number is returned if the calling object is less than the argument, and apositive number is returned if the calling object is greater than the argument.

The methods toUpperCase() and toLowerCase() convert any String to its uppercaseor lowercase equivalent.

The indexOf() method determines whether a specific character occurs within aString. If it does, the method returns the position of the character.The return valueis -1 if the character does not exist in the String.

The endsWith() and startsWith() methods each take a String argument and returntrue or false, depending on whether or not a String object ends with or startswith the specified argument.

The replace() method allows you to replace all occurrences of some character

within a String.

The toString() method converts any primitive type to a String.

You can join Strings with other Strings or values by using a plus sign (+); thisprocess is called concatenation.

You can extract part of a String with the substr ing() method, which takes two argu-ments, and a start and end position, both of which are based on the fact that aStrings first position is position zero.

If a String contains all numbers, you can convert it to a number.

The parseInt() method takes a String argument and returns its integer value. The Double.valueOf() method converts a String to a Double object; the

doubleValue() method converts a Double object to a double variable.

To circumvent some limitations of the Str ing class, you can use the StringBufferclass.You can insert or append new contents into a StringBuffer.



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Review Questions 225

REVIEW QUESTIONS1. A sequence of characters enclosed within double quotation marks is a

.

a. symbolic string

b. literal stringc. prompt

d. command

2. To create a String object, you can use the keyword .

a. object

b. create

c. char

d. new

3. A String variable name is a .

a. reference

b. value

c. constant

d. literal

4. Objects that cannot be changed are .

a. irrevocable

b. nonvolatile

c. immutable

d. stable5. If you declare two String objects as String word1 = new

String("happy"); and String word2 = new String("happy");, thenthe value ofword1 == word2 is .

a. true

b. false

c. illegal

d. unknown

6. If you declare two String objects as String word1 = new

String("happy"); and String word2 = new String("happy");, thenthe value ofword1.equals(word2) is .

a. true

b. false

c. illegal

d. unknown


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7. The method that determines whether two String objects are equivalent, regardlessof case, is .

a. equalsNoCase()

b. toUpperCase()

c. equalsIgnoreCase()d. equals()

8. If a String is declared as String aStr = new String("lima bean");,then aStr.equals("Lima Bean"); is .

a. true

b. false

c. illegal

d. unknown

9. If you create two String objects using String name1 = new

String("Jordan"); and String name2 = new String("Jore");, thenname1.compareTo(name2) has a value of .

a. true

b. false

c. -1

d. 1

10. If String myFriend = new String("Ginny");, then which of the followinghas the value 1?

a. myFriend.compareTo("Gabby");

b. myFriend.compareTo("Gabriella");

c. myFriend.compareTo("Ghazala");

d. myFriend.compareTo("Hammie");

11. If String movie = new String("West Side Story");, then the value ofmovie.indexOf('s') is .

a. true

b. false

c. 2

d. 3

12. The String class replace() method replaces .

a. a String with a character

b. one String with another String

c. one character in a String with another character

d. every occurrence of a character in a String with another character



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Review Questions 227

13. The toString() method converts any to a String.

a. character

b. integer

c. float

d. all of the above14. Joining Strings is called .

a. chaining

b. joining

c. linking

d. concatenation

15. The first position in a String .

a. must be alphabetic

b. must be uppercase

c. is position zero

d. is ignored by the compareTo() method

16. The substring() method requires arguments.

a. no

b. one

c. two

d. three

17. The method parseInt() converts a(n) .

a. integer to a Stringb. integer to a Double

c. Double to a String

d. String to an integer

18. The difference between int and Integer is .

a. int is a primitive type; Integer is a class

b. int is a class; Integer is a primitive type

c. nonexistent; they both are primitive types

d. nonexistent; both are classes

19. For an alternative to the String class, you can use .

a. char

b. StringHolder

c. StringBuffer

d. StringMerger


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20. The default capacity for a StringBuffer object is characters.

a. zero

b. two

c. 16

d. 32

EXERCISES1. Write a program that concatenates the three Strings:Event Handlers is dedicated,

to making your event, and a most memorable one. Print each String and theconcatenated String. Save the program asJoinStrings.java in your Chapter.07folder on your Student Disk.

2. Write a program that calculates the total number of vowels contained in theString Event Handlers is dedicated to making your event a most memorable

one. Save the program name StringVowels.java in your Chapter.07 folder onyour Student Disk.

3. Write a program that calculates the total number of letters contained in theString Event Handlers Incorporated, 8900 U.S. Highway 14, Crystal Lake, IL60014. Save the program name as StringLetters.java in your Chapter.07 folderon your Student Disk.

4. Write a program that calculates the total number of whitespaces contained in theString [TAB][TAB] , which represents two tabs and three spaces. Save the pro-gram asStringWhite.java in your Chapter.07 folder on your Student Disk.

5. Write a program that converts the variables someInt and someDouble in the

statementsint someInt = 21;

andsomeDouble = 128.04;

to stringsusing the classes Integer and Double. Save the program as ToString.java in yourChapter.07 folder on your Student Disk.

6. Write a program that converts the variables someInt, someDouble, and someFloat inthe statements int someInt = 567;, double someDouble = 48.25;, andfloat someFloat = 443.21f; to strings. Do not use the Integer, Double, andFloat classes to make the conversions. Save the program asToString2.java in yourChapter.07 folder on your Student Disk.

7. a. Write a program that demonstrates that when two identical names are comparedand the case differs, the equals method will return false when making a com-parison. Save the program asComparison.java in your Chapter.07 folder on

your Student Disk.b. Demonstrate that the equalIgnoreCase() method will change the comparison in

question 7a. from false to true.



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Exercises 229

8. Write a program to demonstrate that the compareTo() method returns either apositive number, a negative number, or a zero when used to compare twoStrings. Save the program as Compare.java in your Chapter.07 folder on yourStudent Disk.

9. Write a program to demonstrate the following, based on the statement

String dedicate = "Dedicated to making your event a mostmemorable one":

a. index of D

b. char at (15)

c. endsWith(one)

d. eplace(a, A).

Save the program as Demonstrate.java in your Chapter.07 folder on yourStudent Disk.

10. Create a class that holds three initialized StringBuffer objects: your first name,

middle name, and last name. Create three new StringBuffer objects as follows: An object named EntireName that holds your three names, separated by spaces

An object named LastFirst that holds your last name, a comma, a space, andyour first name, in that order

An object named Signature that holds your first name, a space, your middleinitial (not the entire name), a period, a space, and your last name

Display all three objects. Save the program as Buffer.java in the Chapter.07 folderon your Student Disk.

11. Each of the following files in the Chapter.07 folder on your Student Disk has

syntax and/or logical errors. In each case, determine the problem and fix the pro-gram. After you correct the errors, save each file using the same filename precededwith Fix. For example, DebugSeven1.java will become FixDebugSeven1.java.

a. DebugSeven1.java

b. DebugSeven2.java

c. DebugSeven3.java

d. DebugSeven4.java


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CASE PROJECT

The Tax Advantage Company provides free tax services to residents who cannot calcu-late their personal taxes or pay for calculation by a public tax service.You have beenasked to write a Java program that will calculate an estimated tax for either a single ormarried taxpayer, given a keyboard income entry. After the income is entered, a codestatus S for single or M for married is entered.

The necessary classes are a Tax class with a main() method for keyboard entry of incomeand code status values, and a TaxReturn class to calculate the tax based on the input.

The input values should be passed from the Tax class to the TaxReturn class through theinstantiation of a TaxReturn object. The instantiation could take a form such asTaxReturn aTaxReturn = new TaxReturn(income, status);.

For taxpayers, two tax rates are needed, 15 percent and 30 percent. For single taxpayers,the cutoff rate of 15 percent is $10,000, and 30 percent above $10,000. For married tax-

payers, the cutoff rate is 15 percent for amounts below $20,000, and 30 percent foramounts of $20,000 and above.

Program output should show the code status, income, and the amount of tax. Save theprogram files as Tax.java and TaxReturn.java in the Chapter.07 folder on your

Student Disk.

CaseProject


08 java chapter7

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